linux-kernel - Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of __DO_TRACE

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Message-ID: <20260113142340.xEFFVvni@linutronix.de>
Date: Tue, 13 Jan 2026 15:23:40 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux trace kernel <linux-trace-kernel@...r.kernel.org>,
	bpf <bpf@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v5] tracing: Guard __DECLARE_TRACE() use of
 __DO_TRACE_CALL() with SRCU-fast

On 2026-01-12 09:19:58 [-0800], Alexei Starovoitov wrote:
> > Now if you are saying that BPF will handle migrate_disable() on its own
> > and not require the tracepoint infrastructure to do it for it, then
> > this is perfect. And I can then simplify this code, and just use
> > srcu_fast for both RT and !RT.
> 
> Agree. Just add migrate_disable to __bpf_trace_run,
> or, better yet, use rcu_read_lock_dont_migrate() in there.

Wonderful, thank you.

Is this "must remain on the same CPU and can be re-entrant" because BPF
core code such memory allocator/ data structures use per-CPU data
structures and must use the same through the whole invocation?

I did audit network related BPF code and their per-CPU usage usually had
a local_bh_disable() in the relevant spots.

Sebastian